1. Field of the Invention
The present invention relates to a shift control method of an automatic transmission and, more particularly, to a shift control method of an automatic transmission that prevents busy shifting on roads with severe gradient changes by filtering gradient of the road, which is calculated in real time, and controlling shifting according to the filtered gradient.
2. Description of the Related Art
In general, a shift pattern of a vehicle equipped with an automatic transmission is set according to a vehicle speed and an opening degree of a throttle valve, and the vehicle automatically shifts to a suitable gear according to its driving states based on the shift pattern.
Recently, in order to prevent up-shifting while the vehicle is going downhill, fuzzy logic has been used such that shifting is controlled depending on the gradient of the road.
However, such a shift control method has a problem in that if the vehicle is on a road with alternating uphill and downhill sections, the vehicle continuously down-shifts and up-shifts. This is referred to as “busy shifting.” Busy shifting degrades driving comfort and fuel efficiency.